by CKR
The New York Times and the Washington Post today have stories alleging that North Korea sold uranium hexafluoride to Libya. The evidence for this is said to come from actual measurements done by Department of Energy laboratories. However, the two stories give different, irreconcilable, evidence.
The New York Times says that the measurements were done at the Oak Ridge National Laboratory.
Nuclear intelligence experts said the new clues that implicate North Korea as Libya's supplier involve the fingerprints of uranium isotopes, or different forms of the element. Federal analysts, they said, took samples of the Libyan uranium and compared its isotope fingerprint with those of uranium samples from other countries and, by process of elimination, concluded that the uranium had come from North Korea.Uranium has three main isotopes. The most prevalent is U-238, which accounts for a vast majority of natural uranium. U-235 is rare, but it is prized because it easily splits to produce the bursts of atomic energy that power reactors and nuclear warheads.
To trace the Libyan uranium, the government sleuths focused on an even rarer isotope, U-234. They did so because it turns out that concentrations of that isotope vary widely among uranium deposits and mines around the world.
....
A nuclear scientist who consults for federal intelligence agencies but was unaware of the North Korean finding said analysts could use such U-234 information to track the origin of a uranium sample, much as detectives match fingerprints from a crime scene to archives.
He said the analysts could examine the U-234 concentrations in the Libyan sample and compare it with samples from deposits from around the world. Since Western intelligence agencies have no known samples of North Korean uranium, he added, the analysis would proceed by the process of elimination.
Therefore, the strength of the North Korea conclusion would grow in proportion to the number of samples the scientists had from around the world. It is unknown how many samples exist from various uranium deposits or how many samples the federal analysts scrutinized for signs of similarity.
The Washington Post has a different story. Uranium hexafluoride was sent to Libya by North Korea. But
The determination that North Korea provided the uranium hexafluoride was made by a technical group within the Energy Department. It examined containers obtained from Libya -- which gave up its nuclear programs in a deal with the United States and Britain -- and picked up signatures of plutonium produced at Yongbyon, where North Korea has its nuclear facilities. The U.S. official said that because North Korea probably would have produced much of the uranium hexafluoride at the Yongbyon facility, this was deemed the link that connected the material in the containers to the North Koreans.
This explanation, like the NYT explanation, makes sense by itself. But the two are entirely different.
If the uranium hexafluoride was made from uranium recovered from reprocessing, then the U-234 signal would be scrambled by enrichment for use in reactor fuel or by nuclear processes in the reactor. So comparing U-234 with natural samples would make no sense, particularly if no North Korean samples were available. For the U-234 test to work, the uranium would have to be natural, not processed through a reactor.
The implications of the two are different, too. No enrichment apparatus is necessary to produce uranium hexafluoride from uranium ore, just a chemical processing plant. Plutonium traces in the uranium hexafluoride imply (as the Washington Post says) that North Korea has done reprocessing and may have done enrichment to produce the reactor fuel.
Another possibility for the origin of the uranium hexafluoride is that it could have come from the Soviet Union some long time ago. Soviet uranium processing usually combined ores and concentrates from many geographic sources, so the U-234 test would be less diagnostic and might well not fit any natural samples.